The automotive industry, for a number of years, has desired glass of the color grey (sometimes called xe2x80x9cneutral greyxe2x80x9d) for automotive window applications. At the same time, it is also desirable for transmission in the UV and IR ranges of the light spectrum to be minimized. Moreover, certain Governmental regulations in the automotive industry have been known.to require that visible light transmittance be at least 70% in certain vehicular windows when provided by the original equipment manufacturer of the vehicle (e.g. GM, Ford, Chrysler etc.) in the U.S.A. Accordingly, there exists a need in the automotive industry for a glass which achieves these properties (a similar need may also exist in other industries such as the architectural glass industry).
A glass window or other glass article is said to have the desirable color xe2x80x9cgreyxe2x80x9d when it has a dominant wavelength of from 435 nm to 570 nm (this dominant wavelength range defines the color xe2x80x9cgreyxe2x80x9d herein). Moreover, grey glass preferably has an excitation purity of less than about 4.5%. In certain embodiments, it may be preferable to have a dominant wavelength of from 470 nm to 570 nm, or even from 480-560 nm, with purity of from about 0.2 to 4.5%.
While glass having xe2x80x9cgreyxe2x80x9d color is often desirable, there sometimes also exists a need or desire to achieve certain levels of light transmission defined conventionally by:
Lta as visible light transmission,
UV as ultraviolet light transmission, and
IR as infrared light transmission.
Glass thickness ranges of from about 1-6 mm, more preferably from about 3-4 mm, are typically used when measuring the aforesaid characteristics. These thickness ranges are generally recognized as conventional thicknesses for glass sheets made by the float glass process, as well as recognized thickness ranges in the automotive industry.
For automotive windows (including windshields) it is often desirable for glass to have one or more of the following characteristics at any or all of the aforesaid thicknesses:
Lta: at least about 70%
UV: no greater than about 43%, more preferably no greater than 40%
IR: no greater than about 46%, more preferably no greater than about 42%
Classically formulated grey glasses often include low levels of iron (i.e., less than 0.2% total iron) along with cobalt and nickel oxides. Unfortunately, while this type of glass may achieve satisfactory coloration in certain instances, it typically suffers from undesirable solar characteristics. Certain nickel-free grey glasses combine selenium (Se) and cobalt (Co) oxide with iron oxide, but also suffer from poor solar performance characteristics.
Certain known green solar control float glasses are formulated so as to achieve desirable solar characteristics due in large part to their use of large quantities of total iron (e.g., 0.60 to 0.84% total iron). Unfortunately, the green coloration of such glasses does not always harmonize well with certain exterior automotive paints and tends to sometimes affect vehicle interiors when viewed through the glass.
Commonly owned EP 1 041 050 (see also U.S. Ser. No. 09/277,749) discloses a grey glass composition capable of achieving the aforesaid characteristics, including the desirable color grey. In particular, EP 1 041 050 discloses a grey glass with a colorant portion including 0.5-0.8% total iron (expressed as Fe2O3), 0.5-3.0% Er2O3, and 0.0-1.0% TiO2. Moreover, the colorant portion is said to be xe2x80x9csubstantially free of seleniumxe2x80x9d (Se) and xe2x80x9csubstantially free of cobaltxe2x80x9d (Co). While the grey glass of EP 1 041 050 is an excellent glass, it is sometimes undesirable in that it requires much of the very expensive erbium oxide (Er2O3). Rather large amounts of total iron (expressed as Fe2O3) are also required in many examples.
U.S. Pat. No. 5,264,400 discloses a bronze glass including 0.2 to 3% by weight erbium (Er) in the form of Er2O3. Small amounts of Se and/or Co are also present in certain examples. Unfortunately, the glasses of the ""400 patent are bronze, not grey. This is evidenced by the dominant wavelengths in Table 2 of the ""400 patent, which are all above 570 nm. Moreover, the erbium-inclusive glasses of Examples 1-9 of the ""400 patent require large amounts of cerium (Ce), i.e., 0.40% and greater. Such high amounts of cerium are undesirable. Instead, it would be desirable if cerium could be avoided in such large doses for the following reason. Iron is often introduced into glass in the form of Fe2O3, part of which is reduced to FeO to achieve low IR transmittance values. Cerium, often introduced into glass in the form of CeO2, is known to oxidize divalent iron (Fe 2+) to trivalent iron (Fe3+) either directly or in combination other reducing agent(s) present in the glass melt. Therefore, coexistence of iron oxide and cerium oxide will inevitably lead to a decrease in the concentration of FeO in the glass and thus will reduce the IR absorbing power of the glass.
In view of the above, it is apparent that there exists a need in the art for a new glass composition which overcomes the above problems while achieving one or more of desired grey color and desired solar management property(ies) of the particular industry in which it is to be used.
An object of this invention is to provide a grey glass (i.e., having a dominant wavelength of from 435nm to 570 nm) including a colorant portion which may include from 0.50 to 1.20%, by weight, erbium oxide (Er2O3), and from about 0.35 to 0.50%, by weight, total iron (expressed as Fe2O3).
Another object of this invention is to provide a colorant portion for use in a glass composition (with a soda lime silica or other suitable base glass), the colorant portion comprising (or consisting essentially of in certain embodiments), by weight percentage:
Generally speaking, certain embodiments of this invention fulfill one or more of the aforesaid objects and/or needs by providing a grey colored glass composition comprising:
a base glass portion comprising:
wherein the grey colored glass has a dominant wavelength in the range of from 435 nm to 570 nm. In certain exemplary embodiments, the glass composition is substantially free of cerium and/or nickel. However, in certain embodiments, the amount of Se may be from 0.0 to 0.0010%.